Thermopile



Jan. 23, 1962 Filed Sept. 1, 1959 S. M. BAGNO ET AL THERMOPILE 2 Sheets-Sheet 1 IO\ Why],

L l T h a INVENTORS 4 M. AG 16 IS' I A i 1c 55 e, i 1

THERMOPILE Filed Sept. 1, 1959 2 Sheets-Sheet 2 Fig.8

Tu T

a s, 'AsAl...

Array/BY 3,0 3 ,Zill Patented Jan. 23., 1062 3,018,311 TIERMOPILE Samuei M. Bagno, Belleville, Ni, and John H. Fasal,

New York, N.Y., assignors to Walter Kidde & Company, Inc., Beiieville, N.J., a corporation of New York Filed Sept. 1, 1959, Ser. No. 837,452 13 Claims. (Cl. 136-4) The present invention relates to batteries, and more particularly, to thermal batteries, such as lengths of thermopiles adapted for use in fire detecting systems.

The present invention is primarily concerned with, but not limited to, household fire alarm systems which usually comprise one or more heat sensing elements adapted to close an alarm circuit in the event of fire. One of the most important requisites is that such systems be reasonably priced because otherwise home owners and tenants will not purchase them. In order to keep the price as low as possible, that practice has been to use conductors which are separated by a low melting point material which due to the heat of a fire will melt and allow the conductors to make contact and close the alarm circuit. Such heat sensing arrangements are highly unsatisfactory because they operate only after a considerable fire is in progress to supply the heat required to melt the material which separates the conductors, whereby the alarm is given after the fire has had a good start and usually is of such proportions that fire extinguishers designed for home use are ineffective to extinguish the fire. In order to provide a safe household fire alarm system, it is obvious that more sensitive and rapid heat sensing devices, such as a thermopile, be employed. However thermopiles as presently constructed are too expensive so that their use for household fire alarm systems is ruled out.

Accordingly, the principal object of the present invention is to provide an extremely simple and inexpensive thermopile which can be manufactured and assembled in continuous lengths by entirely automatic machinery, if desired, and therefore can be sold at a cost which enables the same to be used for household fire alarm systems.

Another object is to provide such a thermopile which is highly sensitive and completely reliable.

A further object is to provide a practical and economical method of making such a thermopile.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

Preferred embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. 1 is a fragmentary plan view of a strip composed of dissimilar metals which in response to heat generate an electromotive force.

FIG. 2 is a fragmentary plan view illustrating a layer of insulatingmaterial applied to one side of the strip.

FIG. 3 is a plan view of the composite strip after being formed with slots and slits.

FIG. 4 is a plan view of the strip shown in FIG. 3 after being pleated.

FIG. 5 is an enlarged end view of a portion of the pleated strip as seen along the line 5-5 on FIG. 4.

FIG. 6 is an enlarged sectional view taken along the line 66 on FIG. 4.

FIG. 7 is a fragmentary plan view of a completed thermopile in accordance with the present invention.

FIG. 8 is a sectional view taken along the line 88 on FIG. 7.

While only a small section of the thermopile is shown, it is to be understood that actually it is produced in continuous, indefinite lengths and can be coiled or spooled to enable it to be installed in such lengths as required for each particular installation.

Referring to the drawings in detail, a strip 10 is shown in FIG. 1 which is composed of two edgewise joined lengthwise extending sections 11 and 12 of dissimilar metals such as nickel and iron, for example. This strip may have a thickness of about 0.002 inch and a width of about one inch, and can be produced economically by butt welding a block or bar of nickel and a block or bar of iron together and rolling down the composite block to the desired thickness and width.

In FIG. 2, the strip 10 is shown after a layer 14 of thin paper or other heat and electrical insulating material has been applied on one side thereof. The paper may be as wide as the strip or may be slightly narrower than the strip with its edges evenly spaced from the edges of the strip as shown. The primary purpose of the paper layer is to provide adequate covering or insulation at certain portions of the strip to establish hot and cold junctions. The paper layer 14 can be readily applied to the bimetallic strip 10 by automatic machinery including roller means for adhesively coating the strip and/or the layer and roller means for pressing the strip and the layer together to adhesively secure the same.

In FIG. 3, the composite bi-metallic and paper strip is shown after forming substantially rectangular evenly spaced slots 15 at one edge thereof, preferably the edge at which the metal of higher resistivity is located, that is, the iron section 12 of the bi-metallic strip 10 in the illustrative embodiment. These slots extend widthwise beyond the junction of the metallic sections 11 and 12 to provide intermediate portions 16 having a lengthwise dimension at least equal to but less than twice th lengthwise dimension of the slots. For example, a slot dimension of about .250 inch and an intermediate portion dimension of .375 inch may be used.

In FIG. 3, the composite strip is also shown with slots or slits 17 formed at the other edge which extend widthwise beyond the junction of the metallic sections 11 and 12 and are located at lines A, C, E, G and I passing through the lengthwise midpoint of the intermediate portions 16. The width of the slits 17 or the shape thereof is not important so long as the bi-metallic strip is sepa rated and is out of electrical contact at these points.

For example, if the strip 10 has a width of about one inch, the slots 15 and slits 17 preferably extend widthwise about 0.6 inch. It will be appreciated that the slotting and slitting operations can be readily performed continuously by automatic machinery.

In FIGS. 4, 5 and 6, the composite strip is shown after being Z-pleated to provide a thermopile having hot and cold junctions. This is accomplished by folding the intermediate portions 16 in one direction at the slits 17, that is, on lines A, C, E, G and I, with the portions of the paper layer on the folded intermediate portions being in contact with each other, and by folding the composite strip in the opposite direction at the side of the next slot 15 closest to the preceding slit 17, left to right as viewed, that is, on lines B, D, F, H and I, whereby only portions of the metallic sections 11 and 12 are exposed on the side of the pleated strip shown in FIG. 7.

After pleating, the folded intermediate portions 16 provide pairs of portions 16' having a lengthwise dimension of about inch which pairs are separated by slots 15' now having a lengthwise dimension of about A inch. Here again, the pleating operations can be performed by automatic machinery.

In FIG. 7, the reverse side of the thermopile is shown with the lines A to I applied to correlate the same with the side shown in FIG. 4. In order to render the thermopile more sensitive to radiated heat, the side here shown is darkened adjacent the junction of the metallic sections 11 and 12. This can be accomplished by applying a stripe 18 of black paint, preferably by means of automatic machinery.

Also, as shown in FIG. 7, the thermopile is maintained in its pleated condition 'by encasing the edges thereof. This is readily performed with automatic machinery by applying contact tape 19 formed into a U (FIG. 8) at the edges and causing the tape to be adhered to the thermopile by the application of pressure.

Finally, when the thermopile has been cut to a desired length and is about to be installed, terminals such as wires 20 are soldered to the endmost folded intermediate portions at the metallic section 12 thereof.

The thermopile shown and described herein functions to create an electromotive force because of the manner in which the composite strip is slotted, slitted and pleated. For example, if the strip shown in FIG. 3 is pleated as shown in FIG. 7 and the front thereof is exposed, alternate junctions of the portions 16' are exposed and the other junctions will be covered whereby alternate junctions will be hot and cold and the exposed portions of dissimilar metals will be positive and negative with respect to each other to provide the thermopile.

A one foot length of thermopile constructed as shown herein was tested for sensitivity. It Was found that the heat of a burning paper match from a match booklet of the ordinary size when held at a distance of about six inches was instantly detected and caused the thermopile to generate .001 volt which was read on a meter.

From the foregoing description it will be seen that the present invention provides an efficient, practical and reliable thermopile which can be made by mass production methods at an extremely small cost.

As various changes may be made in the form, construction and arrangement of the parts herein, without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense.

We claim:

1. The method of making a thermopile from a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of the section which method comprises forming substantially rectangular evenly spaced slots at one edge of the composite strip extending beyond the junction of the sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of the sots, forming slits at the other edge of the strip extending beyond the junction of the sections and being located on a line passing through the lengthwise midpoint of the intermediate portions, and pleating the strip by folding the intermediate portions in one direction at the slits with the portions of insulating material on the folded portions being in contact with each other and by folding the strip in the opposite direction at the side of the next slot closest to the preceding slit.

2. The method of making a thermopile from a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of the sections, which method comprises forming substantially rectangular evenly spaced slots at one edge of the composite strip extending beyond the junction of the sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of the slots, forming slits at the other edge of the strip extending beyond the junction of the sections and being located on a line passing through the lengthwise midpoint of the intermediate portions, pleating the strip by folding the intermediate portions in one direction at the slits with the portions of insulating material on the folded portions being in contact with each other and by folding the strip in the opposite direction at the side of the next slot closest to the preceding slit, and encasing the edges of the strip to maintain the strip in its pleated condition.

3. The method of making a thermopile from a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of the sections, which method comprises forming substantially rectangular evenly spaced slots at one edge of the composite strip extending beyond the junction of the sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of the slots, forming slits at the other edge of the strip extending beyond the junction of the sections and being located on a line passing through the lengthwise midpoint of the intermediate portions, pleating the strip by folding the intermediate portions in one direction at the slits with the portions of insulating material on the folded portions being in contact with each other and by folding the strip in the opposite direction at the side of the next slot closest to the preceding slit whereby only portions of the metallic sections are exposed on one side of the pleated strip, and darkening the exposed metallic sections adjacent their junction.

'4. The method of making a thermopile from a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of the sections, which method comprises forming substantially rectangular evenly spaced slots at one edge of the composite strip extending be yond the junction of the sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of the slots, forming slits at the other edge of the strip extending beyond the junction of the sections and being located on a line passing through the lengthwise midpoint of the intermediate portions, pleating the strip by folding the intermediate portions in one direction at the slits with the portions of insulating material on the folded portions being incontact with each other and by folding the strip in the opposite direction at the side of the next slot closest to the preceding slit whereby only portions of the metallic sections are exposed on one side of the pleated strip, darkening the exposed metallic sections adjacent their junction; and encasing the edges of the strip to maintain the strip in its pleated condition.

5. The method of making a thermopile from a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals, which method comprises forming staggered slots at opposite edges of the strip extending beyond the junction of the sections to provide intermediate portions having a junction thereon, and pleating and folding'the strip lengthwise to cover the junction onalternate intermediate portions on the side facing in the direction in which the thermopile is to be exposed to provide alternate hot and cold junctions on the strip.

6. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of metals having dissimilar resistivities, said strip having staggered slits at opposite edges thereof extending beyond the junction of said sections to provide intermediate portions having a junction thereon, and pleated folds covering alternate intermediate portions on the side facing in the direction in which the thermopile is to be exposed to provide alternate hot. and cold junctions on said strip.

7. A thermopile according to claim 6, wherein the hot junctions have a darkened area to enhance the heat absorbing characteristics of said strip.

8. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of said sections, said strip having substantially rectangular evenly spaced slots at one edge thereof extending beyond the junction of said sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of said slots, said strip having slits at the other edge thereof extending beyond the junction of said sections and being located on a line passing through the lengthwise midpoint of said intermediate portions, and said intermediate portions being folded in one direction at said slits with the portions of insulating material on folded portions being in contact with each other and said strip being folded in the opposite direction at the side of the next slot closest to the preceding slit to pleat said strip whereby only portions of the metallic sections are exposed on one side of the pleated strip.

9. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of said sections, said strip having substantially rectangular evenly spaced slots at one edge thereof extending beyond the junction of said sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of said slots, said strip having slits at the other edge thereof extending beyond the junction of said sections and being located on a line passing through the lengthwise midpoint of said intermediate portions, and said intermediate portions being folded in one direction at said slits with the portions of insulating material on folded portions being in contact with each other and said strip being folded in the opposite direction at the side of the next slot closest to the preceding slit to pleat said strip whereby only portions of the metallic sections are exposed on one side of the pleated strip, and a darkened area on said exposed metallic sections adjacent their junction.

10. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of said sections, said strip having substantially rectangular evenly spaced slots at one edge thereof extending beyond the junction of said sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of said slots, said strip having slits at the other edge thereof extending beyond the junction of said sections and being located on a line passing through the lengthwise midpoint of said intermediate portions, and said intermediate portions being folded in one direction at said slits with the portions of insulating material on the folded portions be: ing in contact with each other and said strip being folded in the opposite direction at the side of the next slot closest to the preceding slit to pleat said strip whereby only portions of the metallic sections are exposed on one side of the pleated strip, and casing means on the edges of said strip for maintaining said strip in its pleated condition.

11. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of dissimilar metals and a layer of heat insulating material on one side of said sections, said strip having substantially rectangular evenly spaced slots at one edge thereof extending beyond the junctions of said sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of said slots, said strip having slits at the other edge thereof extending beyond the junction of said sections and being located on a line passing through the lengthwise midpoint of said intermediate portions, and said intermediate portions being folded in one direction at said slits with the portions of insulating material on folded portions being in contact with each other and said strip being folded in the opposite direction at the side of the next slot closest to the preceding slit to pleat said strip whereby only portions of the metallic sections are exposed on one side of the pleated strip, a darkened area on said exposed metallic sections adjacent their junction, and casing means on the edges of said strip for maintaining said strip in its pleated condition.

12. A thermopile comprising a strip composed of two edgewise joined lengthwise extending sections of metals having dissimilar resistivities and a layer of heat insulating material on one side of the sections, said strip having substantially rectangular evenly spaced slots at one edge thereof extending beyond the junction of said sections to provide intermediate portions having a lengthwise dimension at least equal to but less than twice the lengthwise dimension of said slots, said strip having slits at the other edge thereof extending beyond the junction of the sections of dissimilar metals and being located on a line passing through the lengthwise midpoint of said intermediate portions, and said intermediate portions being folded in one. direction at said slits with the portions of insulating material on the folded portions being in contact with each other and said strip being folded in the opposite direction at the side of the next slot closest to the preceding slit to pleat said strip, the metal having the higher resistivity constituting the edge in which said slots are formed.

13. The method of making a thermopile, which method comprises butt welding two rectangular bars of dissimilar metals, rolling the bars down to a strip of indefinite length and a desired width and thickness having each of the dissimilar metals extending from the center of the strip to its respective side edges, so forming slots in the strip at the side edges that the dissimilar metals have junctions in the sections between the slots which are in series connection with each other, and covering alternate junctions, whereby, when the uncovered junctions are exposed to heat, a potential can be sensed between the ends of the strip.

References Cited in the file of this patent UNITED STATES PATENTS 1,648,700 Simonds Nov. 8, 1927 2,381,819 Graves et al Aug. 7, 1945 2,519,785 Okolicsangi Apr. 22, 1950 2,813,425 Woolley Nov. 19, 1957 

5. THE METHOD OF MAKING A THERMOPILE FROM A STRIP COMPOSED OF TWO EDGEWISE JOINED LENGTHWISE EXTENDING SECTIONS OF DISSIMILAR METALS, WHICH METHOD COMPRISES FORMING STAGGERED SLOTS AT OPPOSITE EDGES OF THE STRIP EXTENDING BEYOND THE JUNCTION OF THE SECTIONS TO PROVIDE INTERMEDIATE PORTIONS HAVING A JUNCTION THEREON, AND PLEATING AND FLODING THE STRIP LENGTHWISE TO COVER THE JUNCTION ON ALTERNATE INTERMEDIATE PORTIONS ON THE SIDE FACING IN THE DIRECTION IN WHICH THE THERMOPILE IS TO BEEXPOSED TO PROVIDE ALTERNATE HOT AND COLD JUNCTIONS ON THE STRIP. 